Notes

Cold air sinks while warm air rises because cold air is denser than warm air. When a lot of cold air sinks, it creates an area of high air pressure where it hits the surface. This high-pressure air flows to an area of low pressure, creating wind. When this air warms, it rises up into the atmosphere.

When warm air rises into the atmosphere, it cools. The density of the air increases as it cools, which eventually creates an area of high pressure and starts the cycle again.



The heat capacity of a substance is the amount of heat energy needed to raise its temperature by 1°C. Water needs to absorb more heat than land to raise its temperature. So, it takes longer than land to heat.



while heat capacity does not depend on the amount of a substance, specific heat does. By definition, specific heat is the amount of heat energy needed to raise the temperature of one gram of the substance by 1°C. A common unit for measuring specific heat is Joule per gram degree Celsius, or .

This sea breeze moves inland because of the uneven heating of land and water.

At night this process reverses. Land cools faster than water. So, the air above land (5) becomes denser than the air above the ocean (2). A high-pressure area builds up inland and causes a land breeze to blow toward the ocean (7). When the breeze blows, it warms as it cuts through the lighter, warmer air over the ocean.

Earth’s tilt causes opposite seasons in the Northern and Southern Hemispheres. However, within a particular hemisphere, there is a wide variation in climate. The climate of an area is defined by its long-term weather conditions. For example, Canada and Florida are both in the Northern Hemisphere, and Canada tends to be a lot colder than Florida in the winter. Why do different parts of the hemisphere experience different temperatures during the same season?

The answer lies with latitude and the angle at which the Sun’s rays hit Earth.

Latitude is a measure of the distance of a location from the equator. Because Earth is spherical in shape, not all places receive equal amounts of sunlight. They receive sunlight based on their latitude. Places that are farther away from the equator receive less sunlight.

The angle at which the Sun’s rays hit Earth contributes to uneven heating on its surface.

The Sun’s rays hit the equator almost directly, as shown in the image (B). The Sun’s rays are concentrated over a small area, resulting in intense heat.

The Sun’s rays hit the poles at an angle (A). The rays spread over a large area of land, resulting in less heat than in areas that are closer to the equator.

The angle at which the Sun’s rays hit the Earth is called their solar incidence.

Polar Zone

The polar zone includes the Arctic and the Antarctic regions. It also includes the northern regions of Canada, Russia, and Europe. These regions have short summers and long, cold winters.

Temperate Zone

The temperate zone includes the region south of the Arctic to the Tropic of Cancer, and the region north of the Antarctic to the Tropic of Capricorn. These regions have a mild climate.

Tropical Zone

The tropical zone includes the region between the Tropics of Cancer and Capricorn. The equator is at the center of this zone. The temperature in this zone is usually high because the Sun’s rays hit this region almost directly.





When you listen to the weather report, you may hear the term “prevailing winds.” Prevailing winds tend to blow in the same direction at a point on Earth’s surface. These winds are influenced by latitude and Earth’s rotation.

To understand how prevailing winds occur, we need to refresh our knowledge of convection—the cycle of hot and cold air in our atmosphere.

Watch the following video to see how Earth’s rotation and the phenomenon of convection combine to create prevailing winds.

Hot air rises and cooll air comes down and it repeats.

As the air in the hadley cell rises it moves toward the north and south Poles. Cooling and sinking air produces high pressure. The circulation of colder air at the poles is known as a polar cell. Polar cells and hadley cells rotate opposite ways. Ferrel cell is between





Warm, moist air rises from regions of low pressure (A). Cool, dry air descends from regions of high pressure (B).
This image provides a comprehensive look at Earth’s convection cells and prevailing winds:

At the poles, cold air sinks and moves toward the equator, creating polar easterlies.
Hot air rises in the Hadley cells. When it cools, it moves back toward Earth as trade winds.
Air also passes through the Ferrel cells, creating the westerlies. Ferrel cells are located between polar and Hadley cells.
Winds blow along a curved path. Earth’s rotation causes wind to bend to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. We call this phenomenon the Coriolis effect.



The ocean current system operates much like a conveyer belt. This predictable flow has a large influence on Earth’s climate.



Ocean currents are controlled by the motion of local winds across the surface (known as a surface current) and by the natural process of convection.

The Sun’s rays warm up the ocean, causing hot water to rise above the colder water because hot water is less dense. When the hot water reaches the ocean surface, it gives off its heat to the surrounding environment and cools. As it cools, it becomes denser and begins to sink. This convection cycle repeats, causing continuous movement of ocean water on a large scale.

Winds play an important part in determining the direction and strength of currents at the ocean’s surface.



Salinity and Ocean Currents
Currents deep in the ocean are controlled by differences in water density. This process is called thermohaline circulation, because it’s driven by the temperature (thermo) and salinity (haline) of water.

Earth’s oceans contain saltwater, but the salinity of the oceans does not stay the same. The natural processes of the water cycle cause an ocean’s salinity to increase or decrease, which affects current flow. Let’s look at these processes.